This invention relates to a container useful for holding (storing) mask, e.g., a Next Generation Lithography (NGL) mask, and preventing dust or other particles from reaching the mask, and to a method of using the container.
Keeping a mask used in the fabrication of integrated circuits clean is critical. Dust or other particles on a mask can cause corresponding spots to be formed on the substrate of an integrated circuit being formed when the mask is illuminated. Such spots will produce an inaccurate reproduction of the mask on the substrate and thereby can reduce yield.
In prior art optical projection printing systems, light is generally projected from a light source through a lens arrangement and then a mask having a predetermined pattern formed thereon that is stored in a pellicle. The image projected from the mask is incident on a substrate having a light sensitive layer, e.g., photoresist, formed on a surface thereof. In this regard, see, for example, U.S. Pat. No. 4,131,363 (Shea et al.), issued on Dec. 26, 1978. The pellicle in such printing systems generally comprises a solid frame for holding a mask, and a transparent thin film that covers an upper opening of the frame. To print a mask pattern, the substrate and the mask within the pellicle are cleaned to remove any dust or particles thereon, and the bottom of the pellicle frame is securely mounted above the substrate around a light sensitive layer thereon to be irradiated. The pattern on the mask within the pellicle is then irradiated to transfer the pattern of the mask onto the light sensitive layer on the substrate. Generally, dust or other particles on the transparent thin film stretched over the pellicle frame is of no concern. This is because the film is positioned a sufficient distance above the mask so that dust or other particles on the film are out of focus when the surface of the substrate is irradiated through the mask with the type of radiation (e.g., Ultraviolet (UV), deep UV, or X-ray radiation) used in the prior art systems. Therefore, such dust or other particles on the surface of the pellicle itself do not affect the printed-pattern on the substrate.
Pellicles used in the prior art photolithography systems are generally secured to the substrate by various techniques such as using an adhesive, vacuum chucking techniques, magnets, and spring loading arrangements to protect the mask area from dust or other particles. In this regard see, for example, U.S. Pat. No. 4,833,051 (Imamura), issued on May 23, 1989. Prior art pellicles also have included various passageways through the sides of the pellicle frame for equalizing atmospheric pressure changes that occur between the protected area within the pellicle and outside of the pellicle while still protecting the protected area within the pellicle from dust or particles. Such passageway arrangements prevent the thin film covering the frame of the pellicle from deforming and contacting the surface of the mask when the pellicle is transported via different altitudes and/or environments. These passageways in the pellicle frame can include serpentine channels or a straight through passageway with filters mounted therein. In this regard see, for example, the Imamura patent cited above, and U.S. Pat. No. 6,055,040 (Sego), issued on Apr. 25, 2000.
For all Next Generation Lithography (NGL) systems where a narrow beam of radiation is used as, for example, electron beam printing technology, keeping a mask clean is critical. However, known pellicle materials are not transparent enough to radiation, e.g., electron beams and extreme ultraviolet radiation, used with NGL systems.
It is desirable to provide a container for holding a, mask that is to be used with NGL systems during transportation, storage, etc. to keep dust and/or particles from depositing on the mask. The design of the container should also reduce the chance of dust and/or particle being deposited on a mask during mask loading and unloading into and out of the container.
The present invention is directed to a container and use thereof for temporarily storing a Next Generation Lithography (NGL) mask in order to keep such a mask clean prior to it being used with, for example, electron beam printing technology.
A first apparatus aspect of the present invention is a container for housing a lithographic mask. The apparatus comprises a first section and a second section. The second section is in contact with the first section with the contacting first and second sections defining a cavity having a size-which is sufficient to house a lithographic mask and provide an air tight seal around the cavity when pressure within the cavity is less than pressure outside the container such that dust and other particles cannot reach a lithographic mask housed in the cavity.
A second apparatus aspect of the present invention is a container for storing a lithographic printing mask. The container comprises a first container section formed, of a sturdy material and a second container section formed of a sturdy material. When the first and second container sections are placed together they define a cavity therein having a size to fixedly house a mask while not contacting a mask pattern on the mask and provide an air tight seal around the cavity when pressure within the cavity is less than pressure outside the container such that dust and other particles cannot reach the mask housed in the cavity.
A third apparatus aspect of the present invention is a container for storing a lithographic printing mask. The container comprises first and second sections. The first container section is formed of a sturdy material and defines a first cavity which is shaped for contacting an edge section of a mask to be stored in the container and covers, but does not contact an area of a mask pattern on the mask when the edge section of the mask is placed in the cavity. The second container section is formed from a sturdy material and defines a second cavity therein having a size which contacts an edge section of a mask to be stored in the container wherein when the first and second container sections are placed together they fixedly house the mask in the first and second cavities and provide an air tight seal around the cavity when pressure within the first and second cavities is less than pressure outside the container such that dust and other particles cannot reach the mask housed in the cavity.
A fourth apparatus aspect of the present invention is a container for storing a lithographic printing mask. The container comprises first and second container sections. The first container section is formed of a sturdy material and defines a first cavity which is shaped for contacting an edge section of a mask to be stored in the container and covers, but does not contact an area of a mask pattern on the mask when the edge section of the mask is placed in the cavity. The second container section is formed from a sturdy material and defines a second cavity therein having a size which contacts an edge section of a mask to be stored in the container wherein when the first and second container sections are placed together they fixedly house the mask in the first and second cavities and provide an air tight seal around the cavity when pressure within the first and second cavities is less than pressure outside the container such that dust and other particles cannot reach the mask housed in the cavity.
A method aspect of the present invention is a method of storing a mask in a container comprising first and second sections which are both cleaned to remove particles thereon. The method comprising the steps of: placing first and second cleaned sections of the container and a cleaned mask in a chamber and reducing the pressure within the chamber to a first pressure level; while the mask is in the chamber which is at the first pressure level, placing the mask in a cavity defined by portions of the first container section such that a mask pattern on the mask does not contact any portion of the first container; while the mask is in the cavity, placing the second container section in contact with the first container section to form the container and to seal the cavity therein from dust and particles and any pressure changes outside the container; and raising the first pressure level surrounding the container to a second higher pressure level to seal and hold the first and second container sections together.
The invention will be better understood from the following more detailed description taken with the accompanying drawing and claims.